Broadcasting system



Jan. 27, 1931-. w. VAN a. ROBERTS 1,790,486

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INVENTOR l WALTER VAI B. ROBERTS TTORNEY Jan. 27, 1931.

W. VAN B. ROBERTS BROADCASTING SYSTEI Filed Sept. 3, 1927 2 Sheets-Sheet2 INVENTOR WALTER VAN B.KDSERTS ATTORNEYl Patented Jan. 27, 1931 UNITEDSTATES PATENT OFFICE WALTER VAN B. ROBERTS, OF PRINCETON, NEW JERSEY,ASSIGNOR TO RADIO COR- PORATION 0F AMERICA, A CORPORATION OF DELAWAREBROADCASTING SYSTEM Application led September 3, 1927. Serial No.217,369.

This invention relates to a broadcasting system, and more particularlyto a toll broadcasting system, in which others than subscribers to thesystem are not able to hear the broadcasted program.

Customarily, the cost of radio pro rams has been borne by a certainsmall num er of advertisers. It seems, however, that the more logicalway of paying for these programs should be by making those who receivebenefits therefrom, that is, those persons owning radio receiverslistening in on the programs, pay for them. Accordingly, I have deviseda system the object of which is to provide means and a method forbroadcasting a radio program which can be heard by only those who havesubscribed to the system.

Unsatisfactory service to non-subscribers I accomplish by radiating awave the carrier of which is suppressed, that is, a wave in which one ormore of the side bands only are transmitted. These side bands whenreceived in an ordinary receiver, when detected, will not give anintelligible response. A desired response may be obtained only when abeat frequency is supplied to the side bands at the receiver whichcoincides with the carrier that has been suppressed at the transmitter.In my system, the beat frequency is supplied over land lines such aselectric power lines, or telephone lines, and for such supply, eachsubscriber is made to pay a certain amount, preferably by paying a fiatrate per month.

My method of broadcasting is not only advantageous as a toll system butit also allows of improved reception in that static and fading arereduced, for the reason that the carrier which is transmitted by wire isnot subject to these annoyances. Another advantage of my system residesin the fact that because of the control of the carrier, that is, of theamplitude ofthe carrier, and because the carrier is not subject tofading or static a more powerful response may be had. For somewhatsimilar reasons, the quality of the received program would also bebettered.

Another advantage lies in the fact that since only carrier frequenciesare transmitted by wire, no distortion can be introduced by the wireline, no matter how sharp a frequency discrimination it may possess.

a My invention has still another advantage, 1n that reception may be hadfrom stations outside of the toll chain of transmitting stations, and inthe fact, that at the receiver, there is the psychological advantage inhaving the receiver operator feel that he is tuning in on the air at alltimes.

Another object of this invention is to provide a broadcasting systemwherein frequency separation between various stations is maintainedconstant. The manner in which this is done will be explained below.

Other objects as well as advantages of my system will be self-evidentfrom the following description of my invention taken in connection withthe accompanying drawing in which:

Fig. 1 shows according to my invention, a system wherein two side bands'are radiated and in which the carrier, the fundamental of a localoscillator, is transmitted by a power line to a receiving set.

F ig. 2 shows according to my invention, a system wherein a single sideband may be radiated and wherein a harmonic of the locally generatedoscillations is used as a carrier and transmitted over a power line to areceiver.

Fig. 3 is a. system, according to my invention in which two side bandsare radiated and in which the carrier is a harmonic of locally generatedoscillations which harmonic is transmitted over power lines to areceiver, and

Fig. 4 shows diagrammatically a preferred plan for carrying out my tollsystem and for maintaining frequency separation between varioustransmitting stations.

Referring to the drawings, and lnore particularly to Fig. l T indicatesa. transmitting station, and R a receiving station adapted for operationunder my toll system. I have also indicated in that figure a localoscillator which may be of any one of the well known types, such as forexample, a high frequency alternator, or a crystal oscillator. Abalanced modulator is also indicated in Fig. 1, which may comprise apair of vacuum tubes, whose filaments are connected together, whoseplates are connected together through an inductance, whose grids areconnected together through a common inductance, high frequcncy energybeing fed from the oscillator shown in Fig. 1 between the midpoint ofthe indnctancc connecting the grids together and the common connectionof the filaments, and audio frequency energy, as indicated being fedinto the inductor connecting the two grids. The output of the modulatoror the .side bands which have frequencies equal to the oscillatorfrequency plus the speech frequency or the oscillator frequency minusthe speech frequency is fed into the amplifier, indicated in Fig. 1,which may be of any well known type such as the resistance coupledthermionic tube type, where it is amplified and then radiated over thetransmitting antenna TA.

Part of the locally generated high frequency energy is fed into a powerline for example, by means of coupling 2. This coupling lnay consist ofa few turns of wire in the lead 1 from the oscillator, and acorrespondingly few turns of wire in the power line. ln many cases, itwill be found sufficient if simply straight portions of the lead 1 andthe power line 4 are laid together for some distance. Similar couplingmeans should be provided at the receiving station as indicated at 6. Atthe receiving station there may also be provided a phase shifter 8,comprising an inductance and an inductance and a capacitance inparallel. If desired, a phase shifter comprising resistances andinductances may be utilized or in fact any other suitable phase shifter.By means of coil 10, and the receiving ant-enna R. A. carrier freqnencyenergy and side band frequency7 energy may be combined at the receivingset.

It will be thus seen that, by the use of my system, no changes will benecessary in the many receiving sets in operation today. The phaseshifter and coupling 6 should be installed by the members of the chainof transmitting stations utilizing my toll system. The subscriber at thereceiving end may then be charged at a fiat rate for being provided withcurrent of the correct carrier frequency.

'hen receivingr an ordinary program from a station not under the tollsystem, the phase shifter coil 10 to the receiving set may be shortcircuited by a suitable switch 12. In each case, with either switch 12open or closed, the receiving set is operated in the usual manner.

lhile Fig. 1 shows a modification which illustrates the underlyingprinciples of my invention, it is unadapted for use where, for example.more programs than one are to be transmitted at more than one station atthe same time, the stations being part of the same toll system. Undersuch eonditions. it will be found advisable to use modifications such asshown for example, in

Figs. 2 and 3. In the transmitting station 'l shown in Fig. 2 there isprovided, as indicated, an oscillation generator and a harmonicgenerator which may be of any of the well known types. By means of theharmonic generator, the transmitter station T is operated on a harmonicof the waves generated by the local oscillator. As another refinement, aside band filter may be placed after the balanced modulator shown inFig. 2 for the purpose of transmitting only 011e side band by means ofelectro magnetic waves from the antenna T. A. At the receiver by meansof the filter coupled to the antenna circuit R. A. and to the power line4, the correct harmonic utilized by the transmitter T may be combinedwith the side band wave received by antenna R. A.

Another transmitting station of the toll system may have allocated to itanother carrier frequency which may be obtained from the same powerlines by suitable filters. By adjusting the filter at the receiving setthis other station in the toll system utilizing a different harmonic forits carrier than that utilized by the transmitter T may be received,with of course the additional adjustments necessary on the receiving setitself. Vhen receiving ordinary programs from transmitting sets not inthe toll chain, the switch 12, as in Fig. l, may be closed and thereceiving set may be operated in the usual manner.

Fig. 3 shows a system similar to the one given in Fig. 2 with theexception that both side bands are radiated and with the additionalfeature that at the receiving set, in addition to the filter, there isadded the phase shifter described in Fig. 1. In view of the descriptiongiven above, of Figs. 1 and 2 further information as to the apparatusand operation of the system shown in Fig. 3 is thought to beunnecessary.

Frequency separation between the various transmitting stations may behad by transmitting by wire the fundamental oscillatory frequencygenerated by the local oscillator to each of the transmitters in thetoll system, each transmitter having its own harmonic generator. Eachtransmitting station will then select widely different harmonics forits. carrier and will radiate a side band or side bands and transmitbywire the carrier used. This method of maintaining frequency separationand an improved way of providing proper carriers to the receivers isillustrated in Fig. 4, the system shown there being adapted fornation-wide or even world-wide use.

X Y and Z represent three transmitting stations transmitting on wavelengths as indicated, in the vicinity of New York, Denver and London,for example. A, B, C, D, E and F represent receivers timed as indicatedin the drawing, A and B located, say Within a wr-.lasciawitwassen?1vradius of a New York substation indicated N. Y. S1, C and D locatedwithin a similar radius of a Chicago substation Chi. S1, and E and Flocated within the same radius of a Paris substation PAR S1. By means ofland lines fr, y, z, and n, c, p the transmitting stations X, Y, Z andthe substations are supplied from a generating station Wr located at,for examplef lashington with 10,000 cycle current.

Each of the transmitting stations and each of the substations generateharmonics utilizing the supplied 10,000 cycle current as a fundamental.By suitable filters each station will transmit side bands of asuppressed harmonic of the supplied 10,000 cycle current. Thus, asindicated, X will transmit on a suppressed 66th harmonie, Y on the 96thand Z on the 74th suppressed harmonic.

At each substation there will also be generated harmonics utilizing thesupplied 10.000 cycle current as a fundamental. These will be suppliedover power or telephone lines a, I). e, d, e. f to the various consumersor subscribers to the system. Each of the receiving sets will then becoupled in the manner shown in Fig. 3 to the power lines for obtainingthe correct carrier to combine with the received side bands.

The lines transmitting the 10,000 cycle current may, as indicated in theforegoing paragraphs be power. telephone, telegraph lilies or submarinecables or the like. If desired. the 10,000 cycle current may betransmitted by directional antenna to each of the transmitting stations.However, it will be found more feasible and hence it is preferred thatthe fundamental frequency be transmitted by means of conductors.

The system has a decided advantage over wired wireless in that theether. over which the side bands are radiated, does not accentuatecertain frequencies but transmits them all alike. The fact that theconducted harmonics may be distorted by the land lines is immaterial.since at the receiving set, a single harmonic is filtered out whosestrength may be varied as indicated in Fig. 2 by varying the coupling tothe power line, or by varying the coupling from the output side of thelilter, or as indicated in Fig. 3 by means of a phase shifter, or by anyother' means that will readily suggest themselves to those skilled inthe art.

It is to be understood however, that this system for frequencyseparation may he used for the transmitting stations alone. that is,with a slight modification a part of my system may be used for ordinarybroadcasting where no charge is exacted for the program transmitted.When so used `the substations and harmonic generators there may bedispensed with, as Well as the coupling means to the land lines at thevarious receivers. In

this manner, frequency separation between the transmitting stations ismaintained Without any possibility of overlapping However, when usingthis method of frequency separat-ion in connection with the otherelements of my toll system, improved reception will result. By havingthe harmonics generated at various substations, the difficultiesinvolved in transmitting high frequencies (the harmonics) will belessened, since they will be conducted only relatively short distancesfrom the various substations. lt is clear then, that at the receiver thestrength of the carrier may be made large and even though the receivedside band energy is small, the signal heard will be strong since thestrength of the heard signal will be proportional to the product of theside band strength and carrier strength.

The fundamental, or 10,000 cycle supply being of relatively lowfrequency, no difficulty will be met in transmit-ting it to the variousbroadcasting stations and substations.

In other words, by the use of the system shown in Fig. 4 lessening ofboth the side band energy and the carrier energy when transmitting overlong distances is prevented. lVhile the side band amplitude maydecrease. the carrier by means. of the substations is left high. and asa result, distant stations may be very satisfactorily received.

Various changes may be made in the oscillators, or in the harmonicgenerators, filters. modulators, antenuie. phase Shifters, couplings,and connections without departing from the scope of my invention, whosebreadth shall be limited only by the claims which shall follow.

Having thus described my invention, what I claim is:

1. The method of radio transmission which includes the generation. at asingle point. of oscillations, transmitting the oscillations to aplurality of radio transmitting stations utilizing at each of thestations, as a carrier for its transmitted electromagnetic waves, aharmonie of the received oscillations suppressing the carrier at each ofthe stations. radiating only the sidebands to a receiver. and supplyingby conduction the suppressed carrier to the receiver.

2. The method of radio transmission which Aincludes the generation, ata. single point` oi oscillations. conducting the oscillations to aplurality of radio transmitting stations utilizing at each of thestations. as a carrier for its transmitted electromagnetic waves, .aharmonie of the received oscillations. suppressing the carrier andradiating only, at t-he transmitter, sidebands.

n 3. The method of radio broadcasting which includes the supplying to aplurality of radio transmitting stations and to a plurality ofsuhstations of the character described, oscillations from a singlegenerating point, utili`zing as a. carrier at each of the radiotransmitting stations a harmonic of the supplied oscillations,modulating the carrier and trans` mitting from each of the transmittingstations one or more of the resulting side bands only, generating ateach of the substations harmonies corresponding to those utilized by theradio transmitting stations, and supplying by wire to a receiver theharmonics gene vated at the substation.

` 4. In a radio communication system comprising a radio transmitter anda receiver, the transmitter comprising a harmonic generator forgenerating a carrier, a modulator, means for radiating only sidebandscaused by the utilization of the modulator and separate means fortransmitting said carrier; the receiver comprising means for receivingsaid side bands, and separate means for receiving said carrier, saidlast named means including `a filter, a phase shifter and mea-ns forshort circuiting the phase shifter.

5. In a radio transmission system, a supply station having means forgenerating oscillations, a. plurality of radio transmitting stations,means for transmitting said oscillations to said plurality oftransmitting stations, means at each of said stations for generatingharmonics of said oscillations, means for utilizing at each of saidstations an individual predetermined harmonic of said oscillations as acarrier for its transmitted electromagnetic Waves, a carrier Wavesuppressing device and meansl at each of said stations for radiatingonly sidebands.

G. In a signalling system a supply station having means for generatingoscillations, a plurality of radio transmitting stations, means fortransmitting said oscillations to .said transmitting stations means ateach of lsaid transmitting stations for translating said transn'iittedoscillations into frequencies of transmission means at each of saidstations for modulating the translated frequencies in accordance withsignals -desired to be transmitted for producing a carrier andsidebands, means for radiating only said side bands, a plurality ofreceiving stations all thereof being connected by conduction with all ofsaid transmitting stations and means for transmitting the carrier fromeach of said transmitting stations to each of said receiving stationseach of said receiving stations having means for receiving anddistinguishing said side bands and means at each of said receivingstations for combining the proper carrier with the proper sidebands.

lVLTER van' B. ROBERTS.

